Hitherto, in a scan type tunnel microscope as a typical example of a scan type probe microscope, an atom-sized rugged configuration on the surface of a sample is measured by use of a probe. For this purpose, the tunnel type microscope incorporates a micromotion mechanism constructed to utilize the piezo-electric elements. This micromotion mechanism is constructed to infinitesimally control a position of the probe by utilizing elongating/shrinking action of the piezo-electric elements. A tripod type micromotion mechanism for the probe includes three pieces of piezo-electric elements, i.e., a piezo-electric element (for the Z-axis) for controlling a distance between the probe and the sample surface and two piezo-electric elements (for the X- and Y-axes) for causing the probe to scan a measurement target area on the sample surface. These piezo-electric elements are elongated and shrunk in the longitudinal directions by applying voltages thereto. Lengths thereof are varied by regulating the applied voltages, whereby the displacements needed can be produced.
In such a micromotion mechanism of the tunnel type microscope, when elongating the two piezo-electric elements for causing the probe to effect scanning by applying the voltages respectively thereto, amounts of displacement within a range where voltages on the order of 0.about.100 V are usable are normally proportionally distributed according to voltage subranges corresponding to scan areas. The amounts of displacement caused in these voltage subranges are presumed. Under this presumption, the piezo-electric elements are driven in these voltage subranges.
On the other hand, for instance, JP, A, 1-174905 discloses a micromotion mechanism for use with a device such as a semiconductor micromotion positioning device in which a space is relatively easily ensured. This micromotion mechanism performs the control to produce the displacements exhibiting a high accuracy and is therefore provided separately with a displacement measuring device for measuring actual amounts of displacement. This displacement measuring device generally involves the use of a laser displacement gauge, an electrostatic capacity type displacement gauge, a strain gauge, etc.